class MapsSafely[A, Repr] extends AnyRef
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def
safeMap[B <: AutoCloseable, That](in: SeqLike[A, Repr], fn: (A) ⇒ B)(implicit bf: CanBuildFrom[Repr, B, That]): That
safeMap: safeMap implementation that is leveraged by other type-specific implicits.
safeMap: safeMap implementation that is leveraged by other type-specific implicits.
safeMap has the added safety net that as you produce AutoCloseable values they are tracked, and if an exception were to occur within the maps's body, it will make every attempt to close each produced value.
Note: safeMap will close in case of errors, without any knowledge of whether it should or not. Use safeMap only in these circumstances if
fnincreases the reference count, producing an AutoCloseable, and nothing else is tracking these references: a) seq.safeMap(x => {...; x.incRefCount; x}) b) seq.safeMap(x => GpuColumnVector.from(...))Usage of safeMap chained with other maps is a bit confusing:
seq.map(GpuColumnVector.from).safeMap(couldThrow)
Will close the column vectors produced from couldThrow up until the time where safeMap throws.
The correct pattern of usage in cases like this is:
val closeTheseLater = seq.safeMap(GpuColumnVector.from) closeTheseLater.safeMap{ x => var success = false try { val res = couldThrow(x.incRefCount()) success = true res // return a ref count of 2 } finally { if (!success) { // in case of an error, we close x as part of normal error handling // the exception will be caught by the safeMap, and it will close all // AutoCloseables produced before x // - Sequence looks like: [2, 2, 2, ..., 2] + x, which has also has a refcount of 2 x.close() // x now has a ref count of 1, the rest of the sequence has 2s } } } // safeMap cleaned, and now everything has 1s for ref counts (as they were before)
closeTheseLater.safeClose() // go from 1 to 0 in all things inside closeTheseLater
- B
the type of the elements produced in the safeMap (should be subclasses of AutoCloseable)
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the type of the output collection (needed by builder)
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the Seq[A] to map on
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a function that takes A, and produces B (a subclass of AutoCloseable)
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a sequence of B, in the success case
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